High frequency press with capacitive tuning

ABSTRACT

A press for applying high frequency welding and cutting energy to a workpiece placed between platens of the press, at either of two work stations at each of which the platens apply pressure and high frequency energy to the workpiece, has control means for independently tuning a generator of the high frequency energy to selected conditions at each work station. A parallel plate capacitor associated with the generator for the high frequency energy has a capacitance adjustable by changing the spacing between the parallel plates to tune the generator. The plates are urged toward each other by a spring and separated from each other by tension in a cable secured to the spring-movable plate. Means for controlling the cable include a camming member and adjustable stop means for shifting the cable in response to the work station locations of the platen to independently adjust the capacitance at each work station.

' United States Patent [191 Brown 1 Jan. 1, 1974 HIGH FREQUENCY PRESSWITH CAPACITIVE TUNING [75] Inventor: Terence J. Brown, Wigston, England[73] Assignee: USM Corporation, Boston, Mass.

[22] Filed: Feb. 14, 1972 [21] Appl. No.: 226,118

[30] Foreign Application Priority Data Feb. 19, 1971 Great Britain4994/71 [52] US. Cl. 219/1053, 219/1081 [51] Int. Cl. B23k 13/02, H05b9/04 [58] Field of Search 219/1053, 10.55, 219/1067, 10.81

[56] References Cited UNITED STATES PATENTS 3,571,550 3/1971 Rose219/1053 2,522,823 9/1950 Hayes et a1. 219/1053 V Prim qry ExqminerJ. V.Truhe' Attorney-Richard B. Megley et a1.

[5 7] ABSTRACT A press for applying high frequency welding and cuttingenergy to a workpiece placed between platens of the press, at either oftwo work stations at each of which the platens apply pressure and highfrequency energy to the workpiece, has control means for independentlytuning a generator of the high frequency energy to selected conditionsat each work station. A parallel plate capacitor associated with thegenerator for the high frequency energy has a capacitance adjustable bychanging the spacing between the parallel plates to tune the generator.The plates are urged toward each other by a spring and separated fromeach other by tension in a cable secured to the springmovable plate.Means for controlling the cable include a camming member and adjustablestop means for shifting the cable in response to the work stationlocations of the platen to independently adjust the capacitance at eachwork station.

3 Claims, 3 Drawing Figures TUNING BACKGROUND OF THE INVENTION Modernindustrial operations have increasingly relied on high frequency weldingand cutting presses to perform a variety of operations on a range ofmaterials. High frequency welding and cutting presses generally engage aworkpiece between platens of a press which apply pressure and highfrequency energy to the workpiece. One type of workpiece material whichresponds favorably to such high frequency treatment is that which issoftenable by heat generated in the material by the high frequencyenergy. The heat softened material may then be cut, welded together orembossed by dies placed between the platens. Polyvinyl chloride andother thermoplastic materials frequently exhibit such high frequencyactivation.

The operation of high frequency generators providing energy to manytypes of high frequency presses is affected by a variety of differentconditions related to the operation of the press. Among these conditionsare the distance separating the platens of the press when high frequencyenergy is supplied to a workpiece, usually a function of workpiecethickness, and the particular material from which the workpiece is made.If a die is required for the particular high frequency operation, thethickness of the die further affects the distance separating theplatens. The particular die material still further affects the operationof the high frequency generator.

It is known that adjustment to the high frequency generator may be madeto match the impedence or tune the output of the high frequencygenerator to the particular spacing, material and other conditions atthe platens of the press so as to maximize the high frequency energysupplied to the workpiece from the generator. Such tuning is difficultto achieve for the wide variety of conditions which may be encounteredin industrial use of a high frequency press. Accordingly, tuning isoften accomplished only after a series of similar pieces have beenoperated upon by the press.

In many industrial applications, however, it is inconvenient to have thepress limited to operations upon one series of articles at a time. Forexample, in operating upon two different types of workpieces which arelater to be assembled into a single article, such use of the pressrequires operating on all of one type of workpiece before work may bestarted on the other complemental workpieces. Production of the finishedarticle must therefore await the entire production run of one typeworkpiece, or a second press must be employed. The productivity of sucha system is unnecessarily restricted and undesirably low for industrialapplication.

Productivity of high frequency presses can be increased by a presshaving a platen movable between two work stations so that an operatormay set up one station while the press is supplying high frequencyenergy and pressure to a workpiece at the other. Such a press isdescribed in U.S. Pat. No. 3,571,550 issued Mar. 23, 1971, in the nameof Rose, et al'. To further increase the productivity of the pressdescribed in the above cited patent, means for independently tuning thehigh frequency generator for operation at each work station wereprovided.

The tuning means in the above recited patent is a transformer having anoutput winding tapped at varying numbers of turns connecting the highfrequency generator and the platens of the press. A switch selects aparticular tap of the secondary winding for connection to the platens ofthe press. This method of tuning the high frequency generator toconditions at the platens of the press is limited to the number of tapsprovided on the secondary winding of the transformer. A furtherlimitation resulted from the high cost of high frequency transformers.

Another known system for tuning a high frequency generator to particularconditions at the platens of a press is to appropriately vary anelectronic component of the high frequency generator. For example, aparallel plate capacitor in an output circuit of the generator may haveits capacitance varied by varying the spacing of the parallel plates ofthe capacitor. For this purpose it is known to use a Bowden cablearrangement in which the tension in a cable connecting a movable plateof the capacitor and a frame of the machine is modified to move theplate of the capacitor. This arrangement permits more continuous tuningof the generator than the transformer arrangement but is not readilyadapted to be automatically set to a predetermined condition at eachstation of a multi-station press.

Where it is desired to use a two-station welding and cutting press, itis additionally desirable to be able to independently tune the generatorto the operating condition of the press platens at each of the workstations. It is further desirable that the high frequency generator be,in effect, automatically tuned to a preset condition in response tomovement of the platen from one station to another.

SUMMARY OF THE INVENTION Accordingly, it is an object of the inventionto provide apparatus for tuning a high frequency generator toindependent, predetermined condition in response to movement of platensof a press from one work station to another.

To this end, the invention provides means responsive to transversemovement of a platen from one work station to another in a press of thetype described in the above recited patent to independently andautomatically tune the high frequency generator to a predeterminedcondition at each work station of the press. A movable plate of acapacitor in the generator is urged by a spring toward a second plate ofthe capacitor. The movable plate is connected to a cable secured at theother end to a frame of the machine. A Bowden cable arrangementcomprising a pulley in engagement with the cable is movable to tensionthe cable to shift the movable plate of the capacitor. The movablepulley is connected to a lever pivoted about a common axis with thepulley. The lever is positioned to engage a pair of adjustable stopmembers for preselecting a position of the lever, pulley and cable and,hence, of the capacitor plate connected to the cable. A camming membersecured to the movable platen of the press is adapted to engage anextended portion of the lever at the work sta tion location of theplaten to move the lever to move the capacitor plate to one of thepreselected positions and to disengage the lever when the platen is atanother work station to permit the lever and capacitor plate to move tothe other preselected position under the urging of the spring. Theplates of the capacitor are thus adjusted to a preselected position inresponse to move-' ment of the platen of the press from one work stationto another to independently tune the generator at each platen workstation.

DESCRIPTION OF THE DRAWINGS A preferred embodiment of the inventionwhich is illustrative of and not a limitation on the invention will nowbe described with reference to the drawings, in

which:

FIG. 1 is a front view of a two-station high frequency welding andcutting press having means for independently tuning the generator inresponse to movement of a platen to each work station;

FIG. 2 is a top schematic view of the press shown in FIG. 1; and

FIG. 3 is a top view on a larger scale of a portion of the means fortuning the generator of the press shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT A high frequency press of thegeneral type described in the above mentioned patent is shown in FIG. 1.The press has a lower platen extending across the press and an upperplaten generally indicated at 12 mounted on a frame 14 of the press formovement from a first work station on the left to a second work stationon the right and shown in phantom. At each work station the upper platencommunicates with a high frequency generator 20. A control, generallyindicated at 22, is effective to control the movement of the platen 12of the press and to control the high frequency energy supplied from thegenerator to the platen of the press at each work station of the platen.For controlling the high frequency energy, the control is provided withknobs 24 which respectively control the high frequency energy suppliedto the platen at the work stations.

FIG. 2 is a top schematic view of the press in which the high frequencygenerator is shown to include a capacitor having a fixed plate 26 and aparallel, movable plate 28 for varying the spacing between the platesand hence the capacitance of the capacitor. The movable plate is mountedon a compression spring 30 which urges the plate toward the fixed plateand is connected to a cable 32 an opposite end segment of whichenters'the control 22. The movable platen 12 is provided with a cammingmember 34 (FIGS. 2, 3) movable with the platen into engagement with anextended portion 36 of the lever 38 when the platen 12 is in the first,left-hand work station and out of engagement with the lever portion whenthe platen is at the second, right-hand work station as seen in FIG. 2.

Referring now to FIG. 3, the extended portion 36 of the lever 38 ismounted on a pivot 40 slidably supported in slots 42 in spaced verticalsheet members forming a part of the control 22. Abutment rollers 44 and46 are secured to the lever at equal distances from but on oppositesides of the pivot 40. The abutment rollers 44 and 46 are respectivelymounted for engagement with lower stop members 48 and 50, and an upperblock 52 separating the sheet members on which the lever is mounted. Apulley 54 is mounted for rotation about the pivot 40 and receives thecable 32 extending from the capacitor. The cable passes around thepulley and is secured by anchor 56 to the block 52.

When the platen I2 isat the first work station, the camming member 34engages the extended portion 36 of the lever to rotate. the leverclockwise (FIG. 3) to move the abutment roller 46 toward the stop member50 and the abutment roller 44 into engagement with the block 52. Afterinitial lost motion while the abutment roller 44 engages the block 52,the camming member continues to move the lever clockwise by sliding thepivot 40 and the connected pulley 54 toward the stop members or downwardas seen in FIG. 3. Movement of the pulley varies the effective length ofthe path of the cable from its anchor 56 in the block 52 to thegenerator 20 and hence tensions the cable to pull the plate 28 of thecapacitor to change the capacitance of the capacitor.

When the platen 12 is at the second work station, the camming member 34is out of engagement with the lever 36 and the spring 30 urges themovable plate of the capacitor toward the other to tension the cable todraw the abutment roller 46 into engagement with the block and theabutment roller 44 into engagement with the stop member 48. As the lever36 shifts the abutment rollers into these engagements, the pivot 40slides with the pulley toward the block 52. Selection of the position ofthe stop members is thus effective to determine or preselect theposition of the movable plate 28 of the capacitor and thus to preselectthe capacitance.

Returning to FIG. 2, high frequency generator 20 comprises an electroniccircuit 57 for generating the high frequency energy for communication tothe press. The generator circuit may be of any of a number of well knowndesigns, such as a Hartley oscillator, having a connected output circuitincluding the capacitor composed of plates 26 and 28. The output circuitwill tune or match the apparent impedence of the generator with that ofthe press when it operates upon a particular workpiece at a work stationof the press. Adjustments in the spacing of the capacitor plates is thuseffective to tune the generator for particular conditions of the press.In an alternative embodiment, the capacitor composed of plates 26 and 28may be in a tank or resonant circuit for the generator which also servesas an output from the generator. The circuit is still designed such thatvarying the space between the plates of the capacitor will vary thecapacitance so as to tune the generator to particular conditions of thepress.

As described in the above mentioned patent the control 22 is effectiveto select the work station and certain other operating conditions of thepress, including initiation of high frequency energy supply. The controlis also provided with means for timing both the application of pressureand high frequency energy to a workpiece on the lower platen.

In addition the control is now provided with the knobs 24 which may berotated to tune the generator to particular conditions at a work stationof the press. So long as the particular conditions remain the same, thatis, so long as similar workpieces are successively operated upon by thepress, the conditions at the platens will remain the same and the presswill remain tuned to the generator as preselected by rotation of theknob 24 of the control.

As already described, the camming member 34 engages the extended portion36 of the lever 38 in the first work station location of the platen tomove the lever 38 to tune the generator. The extent of movement of thelever is varied by rotation of the knobs 24; however, the lateralposition of the platen 12 at the lefthand work station remains the same.Thus, the camming member may jam against the extended portion of thelever if the platen 12 has not reached the work station when movement ofthe lever is stopped. To prevent such jamming, the camming member 34 ispivotally mounted upon a rearward extension 58 of the platen 12. Aspring 60 also connects the platen extension and the camming member toresiliently hold the camming member in its operative position until thelever 38 engages one of the stop members and then yields to permit thecamming member to rotate about its pivot to prevent jamming of thecamming member and lever.

The path of the cable from the movable plate 28 of the capacitor to theanchor 56 includes a direction changing pulley 62 which has a fixed axisand directs the cable toward the movable pulley 54 as seen in FIG. 3.Tension in the cable from the urging of the spring 30 on connected plate28 draws the movable pulley 54 toward the block 52. The commonconnection of the pulley and the lever 38 to the pivot 40 draws thelever into the position shown in FIG. 3 when the spring draws themovable pulley toward the block. The abutment roller 44 then engages thestopmember 48 while the abutment roller 46 engages the block 52 toprevent further counterclockwise movement of the lever and movablepulley 54. The stop member 48 is threadably engaged with a frame of thepress and connected to one of the knobs 24 so that rotation of the knob24 selects the position of an end 64 of the stop member 48 to preselectthe position of the lever and movable pulley and hence of the movableplate 28 of the capacitor. The capacitance of the capacitor at thesecond work station is thus preselected by rotation of the knob 24.

When the platen 12 moves to the left-hand work station as seen in FIG.2, an inclined surface 68 of the camming member 34 engages a thirdabutment roller 70 secured to the extended portion 36 of the lever torotate the lever about its pivot 40 until the abutment roller 46 engagesthe stop member 50 and the abutment roller 44 engages the block 52. Asthe lever rotates about the pivot, the pivot 40 also slides in the slots42 to move the movable pulley 54, also mounted on the pivot 40, awayfrom the block 52. Movement of the movable pulley away from the blockincreases the effective length of the path of the cable 32 from theanchor 56 to the generator to increase the spacing between the plates ofthe capacitor to vary its capacitance. The extent of movement of themovable pulley 54 in the slots 42 isvdetermined by the position of anabutment surface 72 of the stop member 50 which member is threadablyengaged with a frame of the machine and connected to a knob 24. Rotationof a knob 24 thus selects the position of the abutment surface 72 topreselect a spacing of the plates and the capacitance of the capacitor.Thus, at both work stations of the press the spacing and capacitance ofthe parallel plates 26 and 28 of the capacitor are independentlypreselected by rotation of one of the knobs 24 and adjusted in responseto the work station location of the platen 12.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

l. A press comprising: a platen movable from a first to a second workstation, another cooperative platen, a high frequency generatorelectrically connected to the platens, the generator having a capacitor,the capacitance of which is variable by changing the spacing between afixed and a movable plate in spaced relation with each other to tune thegenerator with a predetermined capacitance value at a work station ofthe press, and means responsive to movement to and arrival of themovable platen at each work station location for spacing of thecapacitor plates in the high frequency generator to provide apredetermined capacitance value.

2. A press as in claim 1 wherein the plate spacing means comprises amovable stop member operative on the movable plate for selecting apredetermined capacitor plate spacing for a station and a lost motionmechanism operable by platen movement to and arrival at a work stationfor moving the movable capacitor plate to the stop member selectedspacing from the other plate.

3. A press as in claim 1 wherein the control means comprises: a levermounted on a slidable pivot; adjustable limit stops engageable by thelever, a pulley rotatably mounted on the pivot, a cable anchored to thepress at one end, passing about the pulley and secured to the movableplate of the capacitor at the other end; and a camming member mounted onthe movable platen of the press for engagement with the lever at a workstation location of the platen to rotate the lever on the pivot and toslide the pivot as permitted by the stops to move the pulley, to tensionthe cable to shift the movable capacitor plate.

1. A press comprising: a platen movable from a first to a second workstation, another cooperative platen, a high frequency generatorelectrically connected to the platens, the generator having a capacitor,the capacitance of which is variable by changing the spacing between afixed and a movable plate in spaced relation with each other to tune thegenerator with a predetermined capacitance value at a work station ofthe press, and means responsive to movement to and arrival of themovable platen at each work station location for spacing of thecapacitor plates in the high frequency generator to provide apredetermined capacitance value.
 2. A press as in claim 1 wherein theplate spacing means comprises a movable stop member operative on themovable plate for selecting a predetermined capacitor plate spacing fora station and a lost motion mechanism operable by platen movement to andarrival at a work station for moving the movable capacitor plate to thestop member selected spacing from the other plate.
 3. A press as inclaim 1 wherein the control means comprises: a lever mounted on aslidable pivot; adjustable limit stops engageable by the lever, a pulleyrotatably mounted on the pivot, a cable anchored to the press at oneend, passing about the pulley and secured to the movable plate of thecapacitor at the other end; and a camming member mounted on the movableplaten of the press for engagement with the lever at a work stationlocation of the platen to rotate the lever on the pivot and to slide thepivot as permitted by the stops to move the pulley, to tension the cableto shift the movable capacitor plate.